Abstract
IntroductionCalcium carbonate biominerals participate in diverse physiological functions. Despite intensive studies, little is known about how mineralization is initiated in organisms.ResultsWe analyzed the medaka spontaneous mutant, ha, defective in otolith (calcareous ear stone) formation. ha lacks a trigger for otolith mineralization, and the causative gene was found to encode polyketide synthase (pks), a multifunctional enzyme mainly found in bacteria, fungi, and plant. Subsequent experiments demonstrate that the products of medaka PKS, most likely polyketides or their derivatives, act as nucleation facilitators in otolith mineralization. The generality of this novel PKS function is supported by the essential role of echinoderm PKS in calcareous skeleton formation together with the presence of PKSs in a much wider range of animals from coral to vertebrates.ConclusionThe present study first links PKS to biomineralization and provides a genetic cue for biogeochemistry of carbon and calcium cycles.Electronic supplementary materialThe online version of this article (doi:10.1186/s40851-014-0001-0) contains supplementary material, which is available to authorized users.
Highlights
IntroductionLittle is known about how mineralization is initiated in organisms
Calcium carbonate biominerals participate in diverse physiological functions
We demonstrate that the compound synthesized by OlPKS is secreted in the endolymph and it acts as a nucleation facilitator in otolith mineralization
Summary
Little is known about how mineralization is initiated in organisms. Biominerals are produced by living organisms through genetically controlled biological processes, and confer stability, rigidity, defences and functionality to organisms; examples include grass opal (rice; silicate), shell (shellfish; calcium carbonate), and bone/teeth (vertebrate; hydroxyl apatite) [1,2]. Factors involved in initial step of mineralization have not been definitively identified far, except for a report that glycogens are always found in the core of nascent otoliths [10]. This is in part due to the lack of genetic studies targeting otolith mineralization. While most zebrafish otolith mutants exhibit defects in the number, shape, and position, only a few completely lack otoliths, and in the
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